The present invention relates generally to an apparatus and method for protecting static sensitive devices. Specifically, the present invention relates to enclosing lead formed integrated circuits within an antistatic enclosure so that the integrated circuit (IC) is sufficiently protected from static electricity, chemical contamination, and mechanical deformation.
Manufacturers of ICs and of printed wiring boards (PWBs) which utilize ICs need to provide protection while storing and transporting the ICs prior to installation in PWBs. While the prior art contains various protective schemes, these schemes typically provide inadequate protection from the various types of danger that can harm an IC. To guarantee that a properly manufactured IC will function correctly in a properly designed PWB, the IC needs protection from three types of danger: electrical, mechanical, and chemical.
A rapid discharge of static electricity in the vicinity of the IC presents the major electrical danger. As known in the prior art the use of antistatic materials lessens this danger. However, some carriers, such as those which use conductive foam, inadequately protect against static damage because the total volume surrounding the IC contains a composite of various materials, such as air and foam. The composite therefore exhibits a non-uniform conductivity in the vicinity of the IC. This non-uniform conductivity subjects the IC to excess danger from static originating from various directions and from rapid discharge sections within the carrier itself. Other carriers, such as those made from metals, provide inadequate static protection because they conduct too well, and tend to rapidly discharge.
Additionally, various carriers provide inadequate static protection because they promote excess handling of the IC. The excess handling presents one static danger from the handling itself and another static danger from an increased likelihood that the IC will be removed from its protective carrier where it will then be exposed to static. Such excess handling dangers characterize carriers in which many parts are collectively housed in one carrier so that unneeded parts are handled when a needed part is used. Excess handling also occurs in carriers where the carrier must be opened or the IC removed in order to read any writing printed on the IC.
Impacts and lead bending represent the major mechanical dangers. A typical IC package has a multiplicity of conductive leads attached to a rigid body. The IC chip itself is housed within the body and electrically connected to the conductive leads by very small wires within the body. An impact can harm the IC body by destroying an internal connection or causing a part of the body itself to break off thereby destroying a seal and exposing the internal IC chip to possible contamination. Prior art carriers inadequately protect against impact if they require excess handling of the IC. Excess handling increases the likelihood of dropping, which subjects the IC to an endangering impact when the IC crashes into a hard surface, such as a floor. Prior art carriers which collectively house many ICs in one carrier also pose an impact danger. If the IC is not securely retained in a predetermined position within the carrier, normal handling of the carrier can produce an endangering impact through ICs crashing into each other.
The degree of danger posed from lead bending depends on the type of package used. Various types of packages are known in the art. A Dual-Inline-Package (DIP) represents one commonly used package type. DIP leads form two lines, where each lead has an approximately perpendicular bend so that the leads extend below the IC, perpendicular to the bottom of the IC. Thus, DIP leads insert into corresponding sockets or through corresponding holes in PWBs, which are also perpendicular to the bottom of an installed DIP. Flat packs represent a less commonly used package type. Flat pack leads extend beyond the IC in a plane slightly below and parallel to the bottom of the IC. Thus, flat pack leads solder directly to PWB traces, which are correspondingly located in a plane slightly below and parallel to the bottom of an installed flat pack.
A lead bending danger from breaking the connection between a lead and a small wire internal to the IC body or breaking the seal of the body around the lead exists for DIPs. Prior art carriers that support an IC within the carrier by the leads inadequately protect against this danger. One such carrier supports the IC within a four-wall open container through spring action of the leads against the internal walls of the carrier. The supporting of the IC by its leads tends to stress the junction of the lead and the IC body. Normal handling of a carrier occasionally causes impacts through bumping or dropping. When the lead-to-body junction is stressed any such impact can magnify that stress enough to endanger the internal electrical connection or seal.
This lead bending danger occurs not only through the initial stresses placed on the lead-body junction from the initial bending, but also during the later repair of a bent lead. Furthermore, a static danger occurs through the excess handling required to repair the bend. The prior art carriers which promote excess handling of the IC inadequately protect against lead bends. Excess handling increases the likelihood of the IC being in a situation where lead bends are likely to occur.
The DIP lead bending dangers pose only a portion of the lead bending threats faced by flat packs. Displacing flat pack leads from the position in which they were originally manufactured exposes flat packs to a later possible bad connection. A mere slight horizontal or vertical variation away from a lead's formed position endangers the quality of a solder connection between the lead and a corresponding PWB trace. Thus, any object that contacts a flat pack's leads risks displacing those leads from their formed position. The prior art carriers which place unneeded pressure on flat pack leads, allow flat packs to move within the carrier, contact other ICs, contact the carrier itself, or promote excess handling of the IC inadequately protect flat pack leads from this lead-bending danger.
Contamination of the leads poses a major chemical danger to ICs. Chemical reactions between an IC lead and materials in the IC's environment endanger the electrical connection between that lead and PWB sockets, solder joints, or traces. Prior art carriers which allow the IC leads to directly contact conductive foam risk a possible contaminating chemical reaction between the foam and leads. Other prior art carriers which tightly clamp the IC leads to the carrier risk a possible contaminating oxidation reaction by entrapping moisture between the leads and carrier.